1. Field of the Disclosure
The present disclosure relates generally to ovens circulating heated air. More particularly, the present disclosure relates to an oven that runs on a 208 volt 20 ampere or 240 volt 20 ampere single phase electric service.
2. Description of Related Art
Hot air impingement and microwave radiation are two different ways to heat and cook a food product. Hot air impingement is based on the transfer of heat from hot air having a higher temperature to an object having a lower temperature, changing the internal energy of the air and the object in accordance with the first law of thermodynamics. On the other hand, microwave radiation consists of electromagnetic waves having a typical wavelength of 12.24 cm or 4.82 inches and a frequency of 2,450 MHz, which are capable of causing dielectric heating of water, fat and sugar molecules in a food product.
Initially, microwave ovens and ovens based on hot air impingement were separately developed and commercialized. However, it was later demonstrated that a combination of hot air impingement and microwave radiation used in an oven can facilitate high-speed, high-quality cooking. This led to the development and commercialization of quick-cooking hybrid ovens based on both hot air impingement and microwave radiation and has established a new standard in the high-speed cooking technology sector.
While the technology of combining hot air impingement and microwave heating to achieve high-speed cooking in an oven has by now been well established, the current technology does not address a host of new challenges created by such combination, including the problem of inefficient energy use and consequent suboptimal cooking efficiency in the existing high-speed ovens. The fundamental principle of ovens involves conversion of an available power (e.g., electric power) into heat energy to be directed to and absorbed by a food product in the oven to raise its internal temperature. Accordingly, the optimal cooking efficiency of an oven requires that the amount of heat energy converted from a given power supply be maximized; the amount of the heat energy directed to a food product in the oven be maximized; and the amount of the heat energy absorbed and retained by the food product be maximized. However, the current technology of the high-speed ovens using both hot air impingement and microwave radiation is not directed to achieving such optimal cooking efficiency.
As a food product resides in a hot air environment of an oven, temperature gradients, or several boundary layers, form around the cooler food product. The oven cooks the food product by transferring the heat energy to the food product through these temperature gradients. Forced air convection by, for example, a blower can improve the heat transfer by “wiping away” the temperature gradients around the food product and bringing the higher temperature air closer to the food product. Hot air impingement can further improve the heat transfer by “piercing” the temperature gradients with jets of hot air and bringing the air at higher temperature closer to the surface of the food product. However, significant portions of the electric power and the heat energy from the hot air impingement are lost in the process to the oven walls, various openings, plenums and air blower walls that form the hot air circulation and delivery system of the oven.
Typical construction of a combination microwave and hot air impingement oven capable of cooking a 14 inch pizza might have about 27-33 air inlet holes at the top of the cook cavity, each of about 0.3 inch to 0.5 inch diameter, resulting in a total open surface area of about 4 square inches through which the air leading into the oven cavity passes. It is the passage of the heated air through these relatively small holes at high velocity that results in the hot air jets characteristic of hot air impingement.
Another well-known problem with the technique of hot air impingement is “spotting” in the areas directly impacted by the hot air jets, causing uneven heating or scorching of the surface of the food product. While this problem may be resolved by, for example, reduction in the hot air velocity and/or increase in the diameter of the columns of impinging hot air, such solutions may further reduce the efficiency of the hot air impingement.
In addition, the diameter/cross-sectional area of a column of hot air impingement generally increases as the distance from the hot air jet orifice increases, thereby reducing the efficiency of hot air impingement. While this problem may be solved by increasing the hot air velocity, as discussed above, such solution may further aggravate the spotting problem.
A still further undesirable aspect of conventional ovens using hot air impingement is noise generated by the air impingement. Heated air is forced through openings at a high air velocity and strikes the product that is heated at a high velocity. After striking the product that is heated at a high velocity, the air is drawn out of the oven cavity. The airflow of the air impingement oven causes undesirably high noise levels.
Conventional ovens using infrared elements located inside the oven cavity, such infrared elements typically being located below the product being heated, can collect grease and other particles on a surface below the infrared element. Due to a combination of the close proximity of the infrared element to the grease and the high temperature of the infrared element, the grease and other particles below the infrared element can generate flames that may cause injury to a user or burning of the product being cooked.
In summary, the problem with the current high-speed cooking technology based on a combination of hot air impingement and microwave radiation is that the combination has never been done in a way to optimize the cooking efficiency of the oven. With the suboptimal cooking efficiency in the presence of various sources of inefficiencies in the conversion of electrical power to heat, the currently available high-speed ovens (either commercial models or residential models) require a relatively high level of electric power to operate.
Consumers of food prepared by high-speed ovens have established standards of cook quality, for example, of food texture and temperature, which are necessary for consumers to readily purchase and consume the food products. A service window has also been established in certain sectors of the foodservice industry, or example, fast food, such that food prepared in high-speed ovens must be delivered in a predetermined time period, for example, about 2 minutes, in order to satisfy the customer's service expectations. For example, a 14 inch pizza cooked in over 5 minutes is outside of an acceptable service window for many fast food locations. In addition, during busy times such as breakfast, lunch and dinner, high-speed ovens must be able to cook food items one after another to the same quality standards and in the same service times without requiring a resting period for the oven's operating temperature to recover. Accordingly, high-speed ovens must repeatedly achieve the desirable cook quality within the acceptable service window for a variety of food products, such as, wraps, pizzas and the like. Currently available high-speed ovens require a 208 volt 30 ampere or 240 volt 30 ampere electric service to repeatedly achieve the desirable cook quality of many food items, such as a 14 inch pizza, within the acceptable service window. Reduction of consumption of electric power in currently available high-speed ovens to a 208 volt 20 ampere or 240 volt 20 ampere electric service typically requires either an extension of the cook times beyond the established service window or a recovery period between repetitive cooks, so that the currently available high-speed ovens cannot repeatedly provide the food product within the service window established within the high-speed oven industry for many food items on such reduced electrical supplies.
Accordingly, it has been determined by the present disclosure that there is a need for an oven circulating an airflow of heated air that runs on a 208 volt 20 ampere or 240 volt 20 ampere single phase electric service. It has also been determined by the present disclosure that there is a need for an oven circulating an airflow of heated air having noise levels that are reduced relative to impingement ovens. It has additionally been determined by the present disclosure that there is a need for an oven having an infrared element that reduces flames generated thereby.